It makes sense because Cubase is looking for .vst3 extension and what is finding here is a folder instead of a plugin... so it stop investigating further and doesn't look into the folder where it would have found the plugins.

The second good news for me is that N4 vst2 saved data is loaded as expected into the vst3 instances. So I am finally able to load my previous sessions (9.5.30 and older) into the last Cubase version.

Something remains broken for vst2 (I'm forced to only use vst3 from now) and N4 vst3 installer should change the folder name within C:/common files/vst3/.

It makes sense because Cubase is looking for .vst3 extension and what is finding here is a folder instead of a plugin... so it stop investigating further and doesn't look into the folder where it would have found the plugins.

Yes ... obviously it worked better before version 9.5.40 ... to me sounds like regression ... they shouldn't load folder files in any case.